1. Field of the Invention
The present invention relates to a structure and method for connecting covered wires, by which respective conductors of the covered wires can be connected to each other by making use of internal heating of the wires brought by ultrasonic oscillation. More particularly, it relates to a connecting method for covered wires, which is effective to connect a shield wire with a ground wire.
2. Description of the Related Art
Generally, it is complicated and troublesome to handle a shield wire having a braided wire coaxially disposed around a core line (or core lines) with the deteriorated workability in using the shield wire. As an effective measure for improving the deteriorated workability, there is provided a connecting structure for wires which takes advantage of inside heating due to the ultrasonic oscillation by Japanese Unexamined Patent Publication (kokai) No. 7-320842.
In the publication, there are shown two kinds of covered wires. One is a shield wire which comprises a core line, an inside insulating rind arranged outside the core line, a braided wire as a shield conductor arranged outside the inside insulating rind, and an outside insulating rind. The other is a ground wire consisting of a core line and an outside resinous rind arranged outside the core line.
According to the disclosed method, in order to connect the braided wire of the shield wire with the core line of the ground wire in front of the connector, the shield wire and the ground wire being both connected to a connector, the ground wire is firstly overlaid on the shield wire so as to cross each other at a connection point. Next, the overlapping portions are interposed between upper and lower resin tips. Then, while compressing the upper and lower resin tips from the outside, they are subjected to ultrasonic oscillation by making use of an ultrasonic horn and an anvil. Consequently, both of the outside rinds of the shield wire and the ground wire are molten for elimination, so that the braided wire of the shield wire comes into electrical contact with the core line of the ground wire. Simultaneously, the upper and lower resin tips are mutually welded to each other thereby to seal up the surroundings of the above connecting point.
In this way, according to the above publication, there has been provided the connecting structure where the braided wire of the shield wire and the core line of the ground wire are connected to overlap each other.
Besides the electrical connection between the shield wire and the ground wire, there is disclosed another connecting structure where covered wires are electrically connected by making use of internal heating produced by the ultrasonic oscillation in Japanese Unexamined Patent Publication (kokai) No. 8-78071.
In the disclosed connecting method, two different covered wires are firstly overlapped so as to cross each other. Next, so-obtained overlapping portions of the wires are disposed between an upper resin tip and a lower resin tip and subsequently, the upper and lower resin tips are subjected to the ultrasonic oscillation under pressure from the outside. Consequently, respective outside rinds of the covered wires are molten and removed from the circumference of the overlapping portions, so that both core lines of the wires can be electrically connected to each other. Simultaneously, the upper and lower resin tips are welded into one body, thereby to seal up the circumference of a connection of the core lines.
In common with the above-mentioned publications, however, since the conductors of the covered wires, i.e. the braided wire, the core lines, etc. are simply overlapped and contacted with each other in the integrated and closed resin tips, the resultant connecting structure does easily exhibit dispersion in terms of contact area between the conductors (between the braided and the core line, between the core line and the core line). In other words, the earlier art connecting methods have problems of dispersion in electrical performance at the connection between the conductors.